Electrical monitoring and stimulation of heart action is well known and has been employed to counter a variety of heart disfunctions. Such monitoring and stimulation requires a reliable means of attaching and maintaining proximity of a conducting electrode to the heart wall. This need arises, for example, in securing a pervenous cardiac pacing lead to the inside wall of the right ventricle. There have been many attempts to achieve such a means. One way is by bonding the electrode to the endocardium with an adhesive. The problem with such adhesive bonding is that it may not provide reliable anchoring of the stimulation electrode and may produce an adverse tissue reaction. Another way is by use of a smooth-surfaced harpoon-like device. Here, a temporary anchor is achieved by piercing the heart wall with an absorbable "harpoon" stored within the electrode.
A third way of attaching an electrode to the inner heart wall is by the use of a tined device. Here, the electrode is held in proximity to the wall of the heart by inert tines which extend from the lead adjacent to the electrode and form an acute angle with the electrode body. These tines maintain the electrode in electrical contact with the heart tissue. The problem with this type of tined device is that over time, the tines will stimulate fibrotic tissue growth which will make later removal of the lead more difficult and which may interfere with the pacing threshold as the tines are typically quite close to the electrode's contact point. Additionally, even after the formation of fibrosis around the electrode, the mechanical stresses on the tines, due to myocardial contractions, can cause shifts in the electrode's position and/or additional tissue reaction.
U.S. Pat. No. 4,281,669 provides novel cardiovascular devices or implants (including pacemaker electrodes) which have biocompatibility and hence reduce thrombogenic problems. The pacemaker electrode embodiment is preferably in the form of a rigid, porous metal coating on a dense coherent metal substrate with a network of interconnected pores substantially uniformly distributed throughout the coating. The rigid nature of the metal coating, the strength of the substrate-coating interface and the strength of the particle-particle bond in the coating provide excellent strength and wear resistance characteristics. The formation of a thin, smooth, firmly attached tissue coating on the porous surface allows the electrode to be incorporated into the cardiovascular system. This tissue coating is formed by a combination of colonization by nucleated cells circulating in the blood stream onto the porous surface and subsequent differentiation into other cell types plus true soft tissue ingrowth into the porous surface from adjacent body tissue thereby achieving a more secure attachment than has previously been the case.
Although the porous pacing electrode offers the advantage of improved blood tissue compatibility over a smooth pacing electrode, both require a period of several weeks to months to become firmly attached, during which time another means of attaching the lead to the heart wall is needed.